Error when registering custom auth class

### dlt version

1.6.0

### Describe the problem

Hi,

It seems the custom authentication registration is boken.

When I use, the CustomAuth like bellow, it works:

```
"auth": CustomAuth(
url=dlt.secrets["sources.eurecia.base_url"],
token=dlt.secrets["sources.eurecia.authorization"],
),
```

But when I try to register the same CustomAuth like this, I face a validation error :

```
register_auth("custom_auth", CustomAuth)

"auth": {
"type": "custom_auth",
"url": dlt.secrets["sources.eurecia.base_url"],
"token": dlt.secrets["sources.eurecia.authorization"],
},

```

> dlt.common.exceptions.DictValidationException: In path ./client: field 'auth' expects the following types: AuthConfigBase, Literal, BearerTokenAuth, BearerTokenAuthConfig, APIKeyAuth, ApiKeyAuthConfig, HttpBasicAuth, HttpBasicAuthConfig, OAuth2ClientCredentials, OAuth2ClientCredentialsConfig. Provided value {'type': 'custom_auth', 'url': 'https://api.eurecia.com/eurecia', 'token': 'o*****8'} with type 'dict' is invalid with the following errors:
> For BearerTokenAuthConfig: In path ./client/auth: following fields are unexpected {'url'}
> For ApiKeyAuthConfig: In path ./client/auth: following required fields are missing {'api_key'}
> For HttpBasicAuthConfig: In path ./client/auth: following required fields are missing {'username', 'password'}
> For OAuth2ClientCredentialsConfig: In path ./client/auth: following required fields are missing {'client_secret', 'client_id', 'access_token_url'}
> For AuthConfigBase: In path ./client: field 'auth' expects callable (function or class instance) but got '{'type': 'custom_auth', 'url': 'https://api.eurecia.com/eurecia', 'token': 'o*****8'}'. Mind that signatures are not validated
> For Literal: In path ./client: field 'auth' with value {'type': 'custom_auth', 'url': 'https://api.eurecia.com/eurecia', 'token': 'o*****8'} is not one of: ['bearer', 'api_key', 'http_basic', 'oauth2_client_credentials', 'custom_auth']
> For BearerTokenAuth: In path ./client: field 'auth' expects callable (function or class instance) but got '{'type': 'custom_auth', 'url': 'https://api.eurecia.com/eurecia', 'token': 'o*****8'}'. Mind that signatures are not validated
> For APIKeyAuth: In path ./client: field 'auth' expects callable (function or class instance) but got '{'type': 'custom_auth', 'url': 'https://api.eurecia.com/eurecia', 'token': 'o*****8'}'. Mind that signatures are not validated
> For HttpBasicAuth: In path ./client: field 'auth' expects callable (function or class instance) but got '{'type': 'custom_auth', 'url': 'https://api.eurecia.com/eurecia', 'token': 'o*****8'}'. Mind that signatures are not validated
> For OAuth2ClientCredentials: In path ./client: field 'auth' expects callable (function or class instance) but got '{'type': 'custom_auth', 'url': 'https://api.eurecia.com/eurecia', 'token': 'o*****8'}'. Mind that signatures are not validated

### Expected behavior

_No response_

### Steps to reproduce

Create a fake CustomAuth class that expects both a url and a token parameter.

Then try to register it. You may reproduce the error.

### Operating system

Windows

### Runtime environment

Local

### Python version

3.12

### dlt data source

_No response_

### dlt destination

_No response_

### Other deployment details

_No response_

### Additional information

_No response_